In a wireless communications network, a base station and a mobile station may communicate with each other via a relay station, as needed. Relay stations are designed to extend the coverage of a wireless communication network by receiving and transmitting communications between the base station and cell edge mobile stations. For example, a relay station can receive signals transmitted from a base station, and then transmit those signals to a mobile station, thus, improving the Signal to Noise Ratio (SNR) of transmissions between the base station and the mobile station. A relay station and a base station may transmit the same data and pilot signals to a mobile station over the same channel resources. For example, as part of a Hybrid Automatic Repeat reQuest (HARQ) process, a relay station may be used to boost the SNR for a HARQ re-transmission to a cell edge mobile station.
Relay communication may be transparent or non-transparent. For transparent relay, a mobile station may be unaware of the presence of a relay station, and should continue to behave normally despite the introduction of the relay station. Transparent relay may be used in a wireless network without the need to introduce new signalling mechanisms or channels to enable relay functionality for a mobile station. Mobile stations that are not configured to utilize additional signalling mechanisms or channels to enable relay may be referred to herein as “legacy mobile stations”. Therefore, transparent relay may be backwards compatible with legacy mobile stations. By contrast, non-transparent relay may use additional functionality, such as signalling mechanisms or channels, to enable relay communications with a mobile station. Therefore, non-transparent relay may not be backwards compatible with legacy mobile stations. Similarly, a radio communications standard that does not include features or mechanisms to implement transparent relay may be referred to herein as a legacy standard.
Long Term Evolution (LTE) is a mobile radio communications standard developed by the 3rd Generation Partnership Project (3GPP). LTE-Advanced (LTE-A) is an enhancement of the LTE standardization. Both transparent and non-transparent relay may be supported in a LTE-A system. The LTE-A standard may provide for backwards compatibility with non-advanced (legacy) LTE systems. Transparent relay may be applied to extend coverage for both legacy LTE mobile stations and LTE-A mobile stations. A number of transparent relay scenarios, where the introduction of relay is transparent to a mobile station, are described in R1-082517, Nortel, “Transparent relay for LTE-A FDD”, TSG-RAN1 Meeting #53bis, Warsaw, Poland, June 2008, the entire content of which are incorporated herein by reference. Documents related to LTE and LTE-A are available at <http://www.3gpp.org/article/Ite> and are incorporated herein by reference.
Some 3GPP TSG-RAN1 meeting documents related to relay in LTE-A, which may be relevant to aspects of the present invention, are: R1-082327, Samsung, “Application of network coding in LTE-advanced relay”, TSG-RAN1 Meeting #53bis, Warsaw, Poland, June 2008; R1-082397, Panasonic, “Discussion on the various types of Relays”, TSG-RAN1 Meeting #54, Warsaw, Poland, June 2008; and R1-082470, Ericsson, “Self backhauling and lower layer relaying”, TSG-RAN1 Meeting #53bis, Warsaw, Poland, June 2008, the entire contents of each of these documents are incorporated by reference.